Plant diversity and tree responses following contrasting disturbances in boreal forest

We determined the abundance and diversity of vascular plants in seven types of disturbance in mixed-wood boreal forest. Disturbance treatments included wildfire, natural regeneration after harvest and several methods of silvicultural site preparation. Relative to undisturbed forest, all disturbance treatments increased plant diversity to about the same extent. The abundance of plant growth-forms differed significantly between disturbance treatments. Silvicultural treatments involving soil disturbance (disk-trenching, drum-chopping and blading) had higher cover of grasses and annual forbs; naturally regenerated and Bracke-cultivated treatments contained more perennial forbs and shrubs. Thus, different post-disturbance plant communities established following contrasting types of disturbance. Plant community biomass and tree growth varied among disturbance treatments. Shoot mass of aspen (Populus tremuloides Michx.) and the root mass of all species declined significantly with increasing soil disturbance intensity. Aspen and white spruce (Picea glauca (Moench) Voss) differed in their response to disturbance. Aspen growth was similar among disturbance treatments. In contrast, aspen density was significantly lower in disk-trenched and bladed treatments than in burned or naturally regenerated treatments, and aspen basal area was significantly lower only in drum-chopped treatments. White spruce grew fastest in drum-chopped sites. Burned treatments had the highest recruitment of volunteer spruce seedlings (up to 3200 ha(-1)), but not significantly higher than in other disturbance treatments. Taken together these results suggest that the most intensive silvicultural treatments had the expected effects of reducing aspen abundance and increasing the growth of spruce, but also contained more grasses and forbs and had lower total root mass than burned or naturally regenerating sites. Further work is needed to examine long-term productivity and the persistence of both native and persistent weedy species following contrasting types of disturbance. (C) 2000 Elsevier Science B.V. All rights reserved.